Abstract: An apparatus for servo track writing on a magnetic medium comprises a clock head (12) and a regular head (14). The regular head (14) writes an initial approximation of the clock track so as to leave a small gap between the last written pulse of the clock track and the first pulse of the clock track. Then this gap is measured by gap measurement system (33) and the frequency of clock track is updated using a direct digital synthesis system (35) so as to fill a full clock track during the next writing. The initial clock track is read by regular head (14) and its output signal is supplied to a phase locked loop. The output of the phase locked loop drives a direct digital synthesis system (35), which generates a modified frequency on its output. A signal of this frequency, in turn, is supplied to the clock head (12), which writes a new improved clock track on the disk.

Abstract: An apparatus for testing magnetic heads and disks comprises a phase locked loop (11) with a phase detector (13) formed by an analog-to-digital converter (40) and a digital-to-analog converter (50). A sine wave signal is supplied to an analog input of an ADC (40) and raw data pulses are supplied to the clock input the of ADC. A phase detector (13) detects deviations in the positions of raw data pulses from the zero crossings of the sine wave signal. A PLL (11) locks in the locations of the zero crossings of the sine wave signal and ADC samples constitute instantaneous values of a bit-shift distribution. These values are processed by a DSP (70). The resulting bit-shift distribution is generated during one disk revolution.

Abstract: A positioning device for magnetic head and disk tester comprises a base plate (100) which supports a rotary spindle (170), for rotating a magnetic disk (168) with a medium to be tested or to be used for testing, and a rotary platform (150) which may slide in one direction (A) along guide shafts (106 and 108) attached to the base plate (100). The rotary platform rotatingly supports a tool support (208) which supports a mechanical arm (218). The latter supports a pair of head holders (220 and 222) with respective read-write heads (228 and 222) to be tested or to be used for testing the disk. The positioning device of this type makes it possible to replace the heads in a convenient position unobstructed by other parts. This is achieved by unlocking the tool support (208) from the rotatable platform (150) by pushing down a lock finger (234) and turning the tool support with the head away from the working position.

Abstract: A method and apparatus for measuring the error rate of a magnetic recording device, such as a hard disk storing a set of data. The apparatus has a partial response maximum likelihood data detecting channel (PRML channel) which differs from a conventional PRML channel by including a noise processing unit (66) which is connected between the output of an A/D converter (54) and the input of a sequence detector (60), and a histogrammer (70), which is connected to the output of a noise processing unit. The method consists of estimating a sequence of noise samples received from the output of the A/D converter (54), processing the sequence of noise samples according to a plurality of predetermined sets of processing coefficients, accumulating a plurality of histograms of segregated processed noise samples, and processing the plurality of histograms so as to determine a dependence of a number of errors on a preselected criterion which characterizes a signal-to-noise ratio of the PRML channel.

Abstract: A magnetic head and disk tester which has linear encoders (40 and 42) installed on lateral sides of a carriage (30) which carries a magnetic head (34), movable in a radial direction along a hard disk. Positions of the magnetic head with respect to the hard disk are measured by means of the linear encoders which are arranged on both lateral sides of the carriage. Outputs of the encoders are supplied to an arithmetic unit (45) which calculates the arithmetic mean of the encoder's outputs and transmits the resulting signal via a feedback line (47) to a piezoelectric translator (37). The translator is the final drive element in the carriage-drive system and is used for fine positioning of the carriage. Thus, if during positioning of the magnetic head the latter is installed in an erroneous position, e.g.

Abstract: A method for measuring the error rate of a magnetic recording device, such as a hard disk storing a set of data. The device has a partial response maximum likelihood data detecting channel (PRML channel) which differs from a conventional PRML channel by including a margin separator (58) which is connected between the output of A/D converter (54) and the input of a sequence detector (60). The system may contain a error counter (70) and data recovery units (66 and 68). The method consists mainly of changing the noise level in the samples received from the output of the A/D converter (54) and then counting the errors, and determining a dependence of a number of errors on a preselected criterion which characterizes a signal-to-noise ratio of the PRML channel. The above dependence can be extrapolated for an actual error rate of the channel being tested.

Abstract: A positioning device includes a base platform (100) which bears linear slide mechanisms (102 and 104). Stationary shafts (106 and 108) of the slide mechanisms are rigidly attached to the base platform. Sliding bushings (110 and 112) are mounted into a movable housing (124) whose motion is governed by a first stepper motor (136). The translation range of the housing is limited by a stop post (148) mounted onto the base platform. The housing supports a ball bearing (130), which comprises an outer race (132) and an inner race (134). The inner race is rigidly attached to the housing. The outer race supports a rotatable platform (150). The rotational motion of the outer race of the bearing is governed by a second stepper motor (154). The rotatable platform bears a mechanical arm (172) which holds a transducing head (180) centrally disposed with respect to the bearing.

Abstract: An apparatus for calibration of optical flying-height testers includes a calibrated micropositioner (100), having a base surface (102) which is permanently attached to a flat horizontal platform (106) and a top surface (104). A transducing head (108) is rigidly, but removably, mounted onto the top surface of the micropositioner. A convex bottom surface (114) of a transparent lens (112), supported on screws (116, 118, and 120), is positioned directly above the transducing head. The lens is preloaded against the tips of the screws by springs (124, 126, and 128). A prism (132) is centrally positioned onto a flat top surface (130) of the lens. The prism contains working planes (136 and 138) which serve as light-energy entrance and exit surfaces and a planar bottom surface (142) which maintains optical contact with the flat top surface of the lens.

Abstract: A ball-type clamping mechanism for clamping computer hard disks in a disk tester for accurate measuring of the disk's parameters comprises a cup-shaped support (10) which is installed on a rotating part of the tester and serves to support a computer hard disk (20) which rests on the upper surface of the support. The support has a cylindrical opening (12) with a diameter equal to or slightly greater than the diameter of the disk opening. Slidingly inserted into the support (10) is a cylindrical retainer (26) which carries clamping balls (28) uniformly spaced from each other in a circumferential direction and located in recesses (30) formed in the side wall of the retainer. The balls have a diameter larger than the side wall of the retainer (26). A pull rod (40) passes through the central opening in the bottom wall of the support and carries a clamping cone (42) which is made from a resilient material softer than the material of the balls (28).

Abstract: A magnetic head and disc tester imitates motions of the head on a hard disc drive and comprises a stationary base (22), a slide mechanism (24) which can be installed in any required position on the base (22) with respect to a center of rotation of a magnetic disc (D). The disc (D) is rotatingly supported by a spindle unit (42) fixed to the stationary base (22). A magnetic head (52) to be tested is attached to the end of an arm (16) which is pivotally supported on a slide (36) of the slide mechanism. The angular position of the longitudinal axis of the magnetic disc with respect to a tangent to a given track of magnetic disc (52) , i.e., a skew angle, can be adjusted and the head can be fixed in the adjusted position. For measuring the parameters of the head or the disc, the slide (36) is moved linearly and carries the magnetic head over the disc in a linear direction, the head being installed at a required skew angle by means of the above-mentioned angular adjustment.

Abstract: A method for data window centering a multifrequency data separator (12) based on having the frequency of a voltage-controlled oscillator (20) at least twice that of read data window frequency, and setting delay of a delay line (14) used in the data separating process so that arriving raw data pulses will be more accurately assigned to their corresponding windows. The method is realized by providing the multifrequency data separator with a phase comparator emulator (30) and a counter (28). According to another embodiment, the apparatus comprises a counter (28b) combined with a delay setting logic unit (40). The method and apparatus described above result in window centering which does not essentially depend on timing characteristics of circuitry used in the construction of the data separator.